''Cerianthus membranaceus'', the cylinder anemone or coloured tube anemone, is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

of large, tube-dwelling anemone in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Cerianthidae Cerianthidae is a family of tube-dwelling anemones in the order Spirularia of the subclass Ceriantharia. Genera The World Register of Marine Species The World Register of Marine Species (WoRMS) is a taxonomic database that aims to provide ...

. It is native to the Mediterranean Sea and adjoining parts of the northeastern Atlantic Ocean.

Description

''Cerianthus membranaceus'' is a large, tube-dwelling anemone. The oral disc can have a diameter of up to . There are two whorls of tentacles, amounting to about two hundred tentacles in all. Those in the outer whorl are long and slender and armed with

cnidocyte A cnidocyte (also known as a cnidoblast) is a type of cell containing a large secretory organelle called a ''cnidocyst'', that can deliver a sting to other organisms as a way to capture prey and defend against predators. A cnidocyte explosively ...

s (stinging cells) and are used for catching prey. Tentacles in the inner whorl are shorter and function to transfer captured food to the central mouth. The tentacles are sometimes banded and come in an array of colours; white, yellow, orange, green, brown, blue, black, purple and violet. The colour of the inner whorl often contrasts with that of the outer whorl. The column of this tube anemone secretes

mucus Mucus (, ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both Serous fluid, serous and muc ...

in which is embedded a unique type of cnidocytes that mesh together to form a fibrous structure. Sand and other particles adhere to this and it forms a leathery, protective tube up to in length. There is no pedal attachment and the lower end of the tube is buried in the soft

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (aquatic environment), the earthy material that exi ...

. The tube is open at the base which allows for escape of water when the animal retreats into the tube.

Distribution and habitat

''Cerianthus membranaceus'' is found on the seabed in shallow water in the

Mediterranean Sea The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern Eur ...

, the northern

Adriatic Sea The Adriatic Sea () is a body of water separating the Italian Peninsula from the Balkans, Balkan Peninsula. The Adriatic is the northernmost arm of the Mediterranean Sea, extending from the Strait of Otranto (where it connects to the Ionian Se ...

and the northeastern Atlantic Ocean, its range extending as far north as Britain. It occurs on sandy or silty substrates where its tube is buried vertically in the sediment. In the Mediterranean, it principally occurs in areas with high levels of organic matter, such as in zones of pollution off

Marseille Marseille (; ; see #Name, below) is a city in southern France, the Prefectures in France, prefecture of the Departments of France, department of Bouches-du-Rhône and of the Provence-Alpes-Côte d'Azur Regions of France, region. Situated in the ...

, where it is present at high densities throughout the year.

Ecology

The tentacles of ''Cerianthus membranaceus'' do not retract, but the whole animal can retreat into its tube. As it does so, some of the tentacles grip the rim and pull the tube closed behind it, effectively making it disappear from view. The tube is normally a permanent home, but if the anemone is disturbed from below, as by a burrowing

sea urchin Sea urchins or urchins () are echinoderms in the class (biology), class Echinoidea. About 950 species live on the seabed, inhabiting all oceans and depth zones from the intertidal zone to deep seas of . They typically have a globular body cove ...

, it can eject itself from its tube, move to a new location and secrete a new tube. ''Cerianthus membranaceus'' feeds on small fish and

plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...

ic organisms which it catches with its tentacles. It is a

protandrous hermaphrodite Sequential hermaphroditism (called dichogamy in botany) is one of the two types of hermaphroditism, the other type being simultaneous hermaphroditism. It occurs when the organism's sex changes at some point in its life. A sequential hermaphrodite ...

, starting life as a male and becoming a female later. The gametes are liberated into the sea and after fertilisation, the developing

larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

e drift with the plankton for a long time before settling on the seabed and undergoing

metamorphosis Metamorphosis is a biological process by which an animal physically develops including birth transformation or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and different ...

into juvenile polyps. The tube is used as a refuge by many

commensal Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit f ...

organisms, especially polychaete worms and

shrimp A shrimp (: shrimp (American English, US) or shrimps (British English, UK)) is a crustacean with an elongated body and a primarily Aquatic locomotion, swimming mode of locomotion – typically Decapods belonging to the Caridea or Dendrobranchi ...

s. The horseshoe worm, ''

Phoronis australis ''Phoronis australis'' is a species of marine horseshoe worm in the phylum Phoronida. It is found in shallow warm-temperate and tropical waters in the eastern Atlantic Ocean and the Indo-Pacific region and was first detected in the Mediterranean ...

'', often attaches itself to the outside of the tube. There may be twenty to fifty horseshoe worms associated with one tube anemone. The lifespan of ''C. membranaceus'' in the wild is not known, but some individuals have been occupants of a tank in Naples Aquarium for more than fifty years.

References

External links

* {{Taxonbar, from=Q876386 Cerianthidae Animals described in 1791